There are known several devices used for extraction of the tool fragments from the root canal of the tooth (U.S. Pat. No. 5,879,160 and U.S. Pat. No. 6,227,855) by means of the mechanical clamp introduced into the canal through the cylindrical tube and ensuring grasping of the fragment. When this technique is used, the clamp is removed from the canal together with the tube and the grasped fragment. A common feature being peculiar both to the present invention and to the aforesaid prior art devices is insertion of the tool into the root canal until it comes in contact with the fragment and extraction of the tool together with the grasped fragment.
However, application of said devices requires undesirable expansion of the root canal up to the stuck fragment, since the fragment should be grasped with the clamp. It is also difficult to control the contact and grasping of the fragment with the tool due to limited access into the narrow root canal (diameter of its opening is about 0.2-1 mm). Besides, since the root canal is often curved, it is rather difficult to transmit mechanical force to the clamp sufficient for reliable grasping of the fragment. Therefore, it is often not possible to reach necessary gripping cohesion between the tool and the fragment stuck in the root canal with certain friction and it can not be removed.
It is known device (US patent application No. 20030124485) similar in its operating principle and used for extraction of the tool fragments from the root canal of the tooth by means of the wire loop introduced into the canal via the cylindrical tube and ensuring grasping of the fragment. However, application of the said device also implies undesirable expansion of the root canal up to the struck fragment. Moreover, it is difficult to attain the necessary gripping between the wire loop and metal fragment of random shape, when the clamping is not controlled.
It is known another device for the extraction of the tool fragments from the root canal of the tooth (U.S. Pat. No. 4,746,292) by means of adhesive introduced into the canal via the cylindrical tube and ensuring adhesion of the fragment to the tube for subsequent extraction. Common feature being peculiar both to the present invention and to said device is introduction of the tool into the root canal until it comes in contact with the fragment and extraction of the tool together with the grasped fragment. However, application of said device requires undesirable expansion of the root canal up to the stuck fragment so that the cylindrical tube could envelop the fragment. Besides, self-hardening adhesive attains required strength rather slowly. Therefore, the patient has to stay in the dental chair experiencing further inconvenience. Moreover, due to the random shape of the fragment and its loose grasping by the cylindrical tube the adhesive may leak into the root canal leading to unacceptable adhesion of the cylindrical tube to the canal walls.
U.S. Pat. No. 4,337,038 is most closely related to the present invention in the entire combination of features and is chosen as the nearest analog. It describes the method and the device for extraction of the tool fragments from the root canal of the tooth by means of electrolytic dissolution of this metal fragment. According to this nearest analog, the first insulated metal electrode in form of cylindrical tube is introduced into the root canal of the tooth stopping short before the metal fragment. Additionally, the second insulated electrode shaped as a needle is also used. It comes through said cylindrical tube and is moved until electric contact with the metal fragment. Physiologically compatible electrolyte is fed into the gap between the fragment and the cylindrical tube. Electropositive potential is applied to the needle electrode and electric current of the physiologically acceptable rate is furnished to the aforementioned electrodes until the fragment is dissolved as a result of the electrolysis.
Common features of the nearest analog and present invention are as follows: at least two insulated metal electrodes are introduced into the root canal until electric contact between one electrode and metal fragment to be extracted, then electric current is applied to the electrodes. However, according to nearest prior art significant current shall be applied to the electrodes for a long period of time, so that to dissolve the metal fragment. As a result, the patient experiences inconveniences. Moreover, due to their high mobility in the solution the dissolved metal cations constituting the fragment and electrolytic anions will be diffused in the surrounding wet tooth tissues, which, as is known, have numerous pores. It may lead to undesirable toxic aftereffects.